This invention relates generally to the field of medical devices, and more particularly to an implantable cardiac rhythm management device which generates electrical pulses.
The heart is generally divided into four chambers, two atrial chambers and the two ventricular chambers. As the heart beats, the atrial chambers and the ventricular chambers of the heart go through a cardiac cycle. The cardiac cycle consists of one complete sequence of contraction and relaxation of the chambers of the heart.
The terms systole and diastole are used to describe the contraction and relaxation phases the chambers of the heart experience during a cardiac cycle. In systole, the ventricular muscle cells are contracting to pump blood through the circulatory system. During diastole, the ventricular muscle cells relax, causing blood from the atrial chambers to fill the ventricular chambers. After the period of diastolic filling, the systolic phase of a new cardiac cycle is initiated. Control over the timing and order of the atrial and ventricular contractions during the cardiac cycle is critical for the heart to pump blood efficiently. Efficient pumping action of the heart requires precise coordination of the contraction of individual cardiac muscle cells.
Implantable cardiac pacemakers have been successfully used to maintain control over the timing and order of the cardiac cycle. In its simplest form, the cardiac pacemaker is an electrical circuit in which a battery provides electricity that travels through a cardiac lead to a cardiac electrode and into the heart causing a contraction, and back to the battery to complete the circuit. Cardiac electrodes are typically implanted within or adjacent one cardiac chamber. This allows for cardiac signals to be sensed predominately from that chamber and for electrical energy pulses to be delivered to that chamber. For example, tip electrodes on transvenous leads are typically implanted in the apex of the right ventricular chamber or at or near the atrial appendage of the right atrium. Because the tip electrode is implanted completely within one cardiac chamber, electrical pulses provided through the tip electrode stimulate the chamber in which the electrode is implanted. So, for example, a pacing pulse delivered to an atrial electrode implanted in the atrial appendage stimulates the atria to contract. Likewise, a pacing pulse delivered to a ventricular electrode implanted in the right ventricle apex stimulates the ventricles to contract.
A current trend in cardiac rhythm management devices, also referred to as implantable pulse generator systems, is to implant cardiac electrodes in and/or through the coronary sinus vein. The coronary sinus vein drains venous blood from the coronary arteries into the right atrium. The coronary sinus vein also allows access to cardiac locations that are adjacent to either the left atrium and/or the left ventricle, where access to the left ventricle is typically gained through the great cardiac vein which is coupled to the coronary sinus vein. As such, the coronary sinus vein is an avenue for accessing, sensing and providing stimulation to different sites of the heart.
One difficulty encountered when using transvenous electrodes implanted within the coronary sinus is that electrical pulses delivered to capture the atrium can also capture the ventricles, or visa versa. This situation is referred to as xe2x80x9ccross capture.xe2x80x9d Cross capture arises from the fact that the coronary sinus is generally located between the atrial chambers and the ventricular chambers along the anterior groove. When transvenous electrodes are positioned in this region of the heart it is possible for electrical pulses intended to stimulate the atrial chamber to instead, or in addition to, stimulate the ventricular chamber. This situation is undesirable, as hemodynamic efficiency is adversely effected when the ventricles contract too soon with respect to the atrial chambers. Thus, a need exists for a reliable way of preventing unintentional cross capture pacing.
The present subject matter provides a system and method to address the aforementioned problems. In one embodiment, the present subject matter utilizes autocapture protocols to monitor the capture of both atrium and ventricle chambers in response to electrical energy supplied to one or more electrodes positioned in or around the coronary sinus vein. Depending upon which chambers of the heart are captured, the present subject matter uses the information to adjust the energy level of pulses supplied to the one or more electrodes. Thus, the present subject matter can be used to prevent unintentional cross capture pacing (i.e., to prevent pulses intended to capture the atria from instead capturing the ventricles, and visa versa).
The present system provides for electrical pulses having a first value to be delivered to a first cardiac region. The system also senses at least one cardiac signal, where the cardiac signal includes indications of cardiac depolarizations resulting from the electrical pulses. In one embodiment, the system detects in the first cardiac signal cardiac depolarizations from a second cardiac region which occurs in direct reaction to an electrical pulse delivered to the first cardiac region. When one or more cardiac depolarizations occurring in direct reaction to electrical pulses delivered to the first cardiac region are detected in the second cardiac region the first value of the electrical pulses are modified so as to eliminate the depolarizations in the second cardiac region caused as a direct reaction to the electrical pulses.
In one embodiment, the first cardiac region is a supraventricular location and the second cardiac region is a ventricular cardiac region, so that the system delivers the electrical pulses to the supraventricular location and detects the cardiac signal from the ventricular cardiac region. Alternatively, the first cardiac region is the ventricular location and the second cardiac region is the supraventricular cardiac region, so that the system delivers the electrical pulses to the ventricular location and detects the cardiac signal from the supraventricular cardiac region.
In one embodiment, threshold test is used to set the first value of the electrical pulses. In one embodiment, test pacing pulses are delivered for the threshold test, where the values of the test pacing pulses are greater than a first value range and include an initial high-test pacing pulse. The cardiac signal is analyzed for cardiac depolarizations from the first cardiac region and the second cardiac region which occur as a result of the initial high-test pacing pulse. The values of the test pacing pulses are then reduced over the first value range until a second cardiac region pacing threshold value is reached where the second cardiac region is no longer depolarized and the first cardiac region is depolarized by the test pacing pulses. The values of the test pacing pulses continue to be reduced over the first value range until a first cardiac region pacing threshold value is reached where both the first cardiac region and the second cardiac region are no longer depolarized by the test pacing pulses. The first value of the pacing pulses is then set based on the first cardiac region pacing threshold value and the second cardiac region pacing threshold value.
In an alternative embodiment, the threshold test includes delivering test pacing pulses, including an initial low-test pacing pulse, at values over a first value range to the first cardiac region. The cardiac signal is then analyzed for cardiac depolarizations from the first cardiac region and the second cardiac region which occur as a result of the initial low-test pacing pulse. The values of the test pacing pulses are then increased over the first value range until a first cardiac region pacing threshold value is reached where the first cardiac region is depolarized and the second cardiac region is not depolarized by the test pacing pulses. The values of the test pacing pulses are continued to be increased over the first value range until a second cardiac region pacing threshold value is reached where both the first cardiac region and the second cardiac region are depolarized by the test pacing pulses. The first value is then set based on the first cardiac region pacing threshold value and the second cardiac region pacing threshold value.
These and other features and advantages of the invention will become apparent from the following description of the preferred embodiments of the invention.